In general, an original signal transmitted by a certain transmitter (hereinafter, simply called a "wanted signal") is always received at a receiving set together with other plural interfering signals. Since the level of distortion in a telecommunication system is determined by the ratio between the power of the wanted signal and total power of all the interfering signals and noises, even if the level of the wanted signal is much higher than each of the interfering signals, the distortion of the communication system can pose a serious problem when the total power of all the interfering signals proportionally increase due to the large number of interfering signals.
In conventional telecommunication systems, interfering signals make it very difficult to extract the information from the wanted signal.
Although an array antenna has been considered as a countermeasure to improve the problems caused by the interfering signals, no practical method of synthesizing the array antenna in an actual telecommunication system has yet been suggested. The problems of applying conventional array antennas, which is based on the method of Eigen-Decomposition, is mainly due to its complexity and operating speed which is too large for real-time processing in telecommunication systems.
The conventional technique about the array antenna was introduced in the following references:
[1] M. Kaveh and A. J. Barabell, "The Statistical Performance of the MUSIC and Minimun-Norm Algorithms for Resolving Plane Waves in Noise," IEEE Trans., Acoust., speech and signal process., vol. ASSP-34, pp. 331-341, April 1986. PA1 [2] T. Denidni and G. Y. Delisle, "A Nonlinear Algorithm for Output Power Maximization of an Indoor Adaptive Phased Array," IEEE Electromagnetic Compatibility, vol. 37, no. 2, pp. 201-209, May, 1995.
The problems in the conventional method of designing array antennas are, first, it requires some knowledge about the location of the wanted signal apriori, and second, it requires so many computations that real-time processing cannot be performed. Especially, when the arrival angle of the wanted signal or the total number of signal sources is unknown, the required amount of computation becomes even larger, which makes it impossible to apply the conventional method of synthesizing the array antenna to the practical signal environment, such as mobile communications.